Direct Excitation of the ²²⁹Th Isomer in Solid-State Hosts

The ^229mTh isomeric state has the lowest energy of all known nuclear excited states, placing it within the reach of current table-top laser technology. This extraordinary property, combined with its long lifetime, should allow for the construction of an optical nuclear clock of incredibly high precision and accuracy, capable of probing the variability of the fundamental constants. Beyond its use in clock systems, the isomer serves as a sensitive probe of its solid-state environment.

I will discuss the first direct excitation of the ²²⁹Th isomer in a LiSrAlF₆ environment, and the laser system used for the excitation spectroscopy. The determination of the isomeric transition energy to spectroscopic precision has opened the door to a new generation of experiments probing the isomer’s behavior in solid-state hosts, including the first instance of laser-induced conversion electron Mössbauer spectroscopy (CEMS) in ThO₂. These studies represent a rapidly growing interdisciplinary field that pulls in distinct concepts from nuclear physics, quantum chemistry, materials science, condensed matter physics, and AMO physics.